Experimental re-evaluation of the γ-ray energy and emission probability for the 159 keV transition in 238U following the α-decay of 242Pu.

Because of the very low specific activity of (242)Pu, the non-destructive assay of this isotope by means of conventional high-resolution gamma-spectrometry (HRGS) is possible only for Pu samples highly rich in (242)Pu. For bulk samples suffering from the gamma self-attenuation and self-fluorescence effects, the only practical choice for the quantitative analysis of (242)Pu is the weak γ-line emitted in the 159 keV transition of its α-decay daughter (238)U. A recent study revealed a significant disagreement between the (242)Pu mass values in a 99.72% enriched (242)PuO(2) sample as reported by HRGS and neutron coincidence counting. This fact motivated the present study on the experimental re-evaluation of the γ-emission probability for the 159 keV transition using a combination of α-, γ- and mass-spectrometry techniques. The obtained new emission probability P(2)=(2.20±0.08)10(-6) turned out to be ≈35% smaller than the currently adopted value. The study also suggested a new value E(2)=159.018±0.016 keV for the energy of the respective γ-ray.

Fast and accurate approach to gamma-spectrum modelling: a validation study with a shielded/unshielded voluminous uranium sample.

gamma-Spectrometry is a basic and widely applied method in nuclear security and nuclear safeguards areas. For addressing the growing needs in education and training, in research and development as well as in practical gamma-spectrometry in these areas, Monte Carlo based web-accessible gamma-spectrum modelling tools have been developed for the European Commission's Nucleonica portal at www.nucleonica.net. A recent validation study has demonstrated a good performance of the implemented simulation approach for modelling realistic gamma-spectra from shielded and unshielded point-like sources. In the present work this approach has been further tested with the use of a 0.2kg voluminous 4.46wt% enriched uranium reference material and a portable 10% HPGe detector. The simulations for shielded and unshielded measurement conditions revealed a good agreement with the experimentally acquired gamma-spectra, both for the detection efficiency values and for the overall spectrum shape and intensity in the energy range up to 2.6MeV.

Testing applicability of black poplar (Populus nigra L.) bark to heavy metal air pollution monitoring in urban and industrial regions.

A comparative study of the capabilities of black poplar-tree (Populus nigra L.) bark as a biomonitor of atmospheric heavy-metal pollution is reported. Performance indicators (concentrations and enrichment factors) of heavy metal bioaccumulation of bark were compared to the corresponding indicators of epiphytic lichens Xanthoria parietina (L.) Th. Fr. and Physcia adscendens (Fr.) H. Oliver, collected simultaneously with bark samples within the Kiev urban-industrial conurbation. The concentrations of 40 minor and trace elements in the samples were measured by a combination of epithermal and instrumental neutron activation analysis (NAA) using a 10 MW nuclear research reactor WWR-M as the neutron source. Statistical analysis of the data was carried out using non-parametric tests. It was shown that for the majority of the elements determined a good correlation exists between their concentrations in bark and in the lichen species. The accumulation capability of the bark was found to be as effective as, and in some cases better, for both types of lichens. Based on the background levels and variations of the elemental concentration in black poplar-tree bark, threshold values for the enrichment factors were established. For a number of elements (As, Au, Ce, Co, Cr, Cu, La, Mn, Mo, Ni, Sb, Sm, Ti, Th, U, V, W) an interspecies calibration was performed. An optimized pre-irradiation treatment of the bark sample was employed which efficiently separated the most informative external layer from the deeper layers of the bark and thus minimized variations of the element concentrations. Results of this study support black poplar-tree bark as an alternative to epiphytic lichens for heavy metal air pollution monitoring in urban and industrial regions, where severe environmental conditions may result in scarcity or even lack of the indicator species.